Nickel cadmium cells have long been the standard for high discharge applications such as power tools. However, increasing emphasis is being placed on nickel metal hydride electrochemical cells as replacements for nickel cadmium cells. Nickel metal hydride cells avoid environmental concerns relating to cadmium and have improved energy density. Nickel metal hydride cells are mainly used with low rate discharge devices such as cellular phones and portable computers due to problems in nickel metal hydride power performance when used with high rate discharge devices.
The shortfalls in power performance characteristics generally occur at high discharge rates and at low temperatures during initial use of existing nickel metal hydride cells. When discharged at a high pulsed rate, for example 18 C (a current in amperes which is 18 times the value of the rated capacity of the cell) as in most power tools, nickel metal hydride batteries known in the art exhibit a voltage polarization during the initial operational discharge. At low temperatures, for example, at or below 0.degree. C., this voltage polarization is even more pronounced and severely limits the power capabilities of the battery. Cycling of the cell or battery that occurs during subsequent charging and discharging may reduce the effects of this polarization, but obviously has no effect on the disabling voltage polarization encountered initially. Consequently, there is a need for enhancing the performance of metal hydride electrochemical cells during the initial operational discharge of the cells.